In general, a secondary battery means a battery that can be recharged unlike a primary battery that cannot be charged and has been prevalently used in small-sized advanced electronic device fields such as cellular phone, PDA, notebook, computer, or the like. In particular, a lithium secondary battery, which has an operating voltage of 3.6V, has three times more than that of a nickel-cadmium battery or a nickel-hydrogen battery mainly used as a power supply for electronic devices and has high energy density per unit weight. Therefore, the use of the lithium secondary battery has been rapidly increased.
Further, the above-mentioned secondary battery may be classified into an internal type battery and an external type battery based on a method of mounting a secondary battery in electronic devices, wherein the embedded type battery is widely referred to as an inner pack. Therefore, the inner pack is used for the embedded type battery in the description hereinafter.
The external type battery forms a portion of the electronic devices. That is, the external battery is mounted in a state in which one surface thereof is exposed to the electronic devices. Therefore, the external type battery may be mounted and separated in and from the electronic device by the relatively easy working, but the appearance thereof needs to match shapes of the electronic devices. As a result, the external type battery should be manufactured to be individually matched with various types of electronic devices. Therefore, the external type battery has low compatibility and is designed to have various types of designs, which leads to the increase in production cost.
For this reason, the use of the inner pack has been recently increased. Therefore, the inner pack is mounted in the electronic devices and the electronic device in which the inner pack is mounted includes a separate cover covering the mounted inner pack from the outside. Therefore, mounting the inner pack in the electronic device is relatively cumbersome. On the other hand, the inner pack may be compatible with several types of electronic devices and may be simply designed due to the above characteristics. As a result, the inner pack may be advantageous in mass production and production cost thereof can be reduced.
Briefly describing the configuration of the inner pack, the inner pack is configured by stacking pouch type bare cells that are one of the core components of the secondary battery, wherein the inner pack is configured by positioning the bare cells in the cell case and then, stacking the cell cases so as to protect the bare cells and easily fix the bare cells.
In this case, the bare cell generates heat at the time of operating. Therefore, the inner pack is provided with a sensing substrate sensing the temperature and voltage of the bare cell so as to monitor whether the stabilized voltage is generated while preventing overheating of the bare cell.
In the related art, the assembly working is not easily performed due to the direct welding of the sensing substrate to each cell or the welding of the sensing substrate to each cell using the terminals. Further, the welding is not uniform according to the welding strength of the worker, which causes a problem in that the welding strength reference is proposed in mass production, the working process is added, or the like.